1214 



SCANDINAVIAN FISHES. 



one, which is said to lia\e its i-oots in the capillaries of 

 the intestinal canal, runs under the stomach and citcum, 

 there ramifying into a capillary network bet^veen the 

 green cells in the wall of the caecum, which is said to 

 functionate as a kind of liver. Here the blood, it is 

 stated, is again collected, on tlie upper side of the cte- 

 cum, in the other, superior canal, whose contractions 

 run backwards in the opposite direction, to the exit of 

 the caecum from the stomach, and convey the blood to 

 tlie heart: — and we sliould tlius liave found here a 

 l)ortal ^'ein (the inferior canal) and an efferent hejjatic 

 vein (the superior canal). Descriptions have besides 

 been given of a separate, but wall-less lymjihatic system, 

 filling all the cavities of the bodj' and ramifying into 

 the smallest lacuna^ between the organs. But in all the 

 said contractile canals there appear distinct traits of the 

 typical arrangement of the vessels in a worm. In those 

 ]iaired connecting vessels between tlie upper vessel and 



y 



Vig. 1370. Anterior end of n Branchiostoma laiiceolatum, seen from 



the right and magnified. After Vogt and Yung. 



a, olfactory depression; b, first, c, second pair of nerves; d, eye spot; 



e, peripheral ganglion cells in the skin; /, notochord; y, spinal cord; 



It, fin-ray growths (spinous processes?); i, myocomma. 



the lower wiiicli are most plentiful in the forej)art of 

 tlie worms (Ainndatu), we may well seek a parallel to 

 the respiratory system of Branchiostoma. And the two 

 contractile vessels that run bulging in the latter along 

 tlie u])per and lower sides of the intestinal canal also 

 functionate in the worm for the tirst sucking up of the 

 alimentary juice and its con\er.siou into nutritive fluid. 

 The vei'tebral segmentation of tlie body is indeed 

 subindicated even in Branchiostoma by a transversal 

 division of the raembrano-cartilaginous sheath that en- 

 velops the notochord, expands both around the neural 



canal and the iuemal cavity, and breaks U]) at the liase 

 of the vertical dermal tin-fold along the dorsal and the 

 posterior jjart of the ventral margin into pieces resem- 

 bling fin-rays (fig. 364, a and h\ fig. 370, /;) — though 

 far more numerous than tlie muscle flakes. But the 

 muscular and nervous systems are the organs that iiere 

 most distinctly call to mind the vertebrate type. 



That portion of the muscular sy.stem M'hich answers 

 to the great lateral muscles of fishes is divided into 

 transverse bands {m/ionieres), which are angular, with 

 the angle directed forwards; and each myomere is com- 

 posed of bundles of muscle fibre extended between ten- 

 dinous expansions of the notochordal sheath {mijocom- 

 mata), just in the manner of the said piscine muscles. 

 Along the ventral side of the abdominal region, between 

 the mouth and the atrial ])ore, extends an horizontal 

 muscular plate, composed of transversal muscle fibres. 

 Its fiuiction, consisting of rhythmical contractions, is 

 mainly subservient to the respiration, and its posterior 

 part, at the atrial pore, swells into the so-called abdo- 

 minal papilla, coursed by muscle fibres in all directions. 



The nervous .system shows the peculiarity that the 

 spinal nerves (except the first two pairs) do not issue 

 in pairs, exactly opposite each other, but alternately, 

 the nerves of one side in front of those of the other 

 (fig. 366, e), and that only the basal parts of the dorsal 

 branches (sensory nerves) are entire, those of the ven- 

 tral (motory) nerves being broken up into fibres. In 

 the spinal cord there appear, as in the preceding order, 

 besides the ordinary ganglion cells, large so-called co- 

 lossal cells. Among the organs of sense A. Retzus was 

 the first" to discover a black pigment spot (fig. 370, (I) 

 on the anterior end of the spinal cord. This spot is 

 interpreted as an e^^e of the most rudimentary descrip- 

 tion. It is com|)aratively larger in young specimens 

 than in old, which suggests a still advancing reduction; 

 and its visual function is somewhat dubious, for similar 

 spots jtlso occur in a row on each side along the greater 

 ]>art of the s])inal cord. Al)ove the anterior end of the 

 S]>inal cord, but on the left side of the body, Kolliker'' 

 and, after him, (^)l:atrefages'" found a ciliated depres- 

 sion (fig. 370, a), the simplest form of an olfactory 

 apparatus. The organs of taste we have already re- 

 marked f)n the cirri of the mouth a])erture and the 

 postoral velum; and a similar cell structure also ajijiears 



" Moniitsl.er. Akad. Wiss. Berlin, 1839, p. 108. 



'■ Miill. Arch. Anat., Physiol., 1843, p. 32. 



<■ Ann. So. Nat., ser. 3, Zool., tome IV (1846), p. 226. 



